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Anime & Manga

In Descendants of Darkness, Hisoka suspects that Tsuzuki is possessed by a demon and tells him, as usual, to bring something to eat for the Chief. He "reminds" Tsuzuki that the Chief hates sweets, and when Tsuzuki falls for it, he knows it's an impostor. (The chief has a notorious Sweet Tooth.)

In From Eroica with Love, Major Eberbach tests if a guide who called him is a KGB spy by asking her about a fictitious aunt. When the guide gets confused, he concludes she's no spy, because a spy would've pretended to know the woman.

Sasuke came up with a very long and convoluted "password" for his two teammates to memorize in case they ever needed confirmation of one another's identity. Naruto leaves to go to the bathroom, and when he comes back, Sasuke asks him to code in. Naruto repeats it back perfectly... and Sasuke decks the imposter, declaring that the real Naruto would never have been able to remember something that long.

Later, the Mizukage does this quite expertly, although her victim is not an impostor, but under control. Ao, possessed by one of Danzo's men, encounters the Mizukage and Chojuro, apologizing to the latter for getting into a position in which he needed help, then asks the Mizukage to remove the seal on his eye. She then points out that Ao would not apologize to Chojuro, and he'd know the sealing tag could not be removed, then punches him when he calls heran old hag, thus restoring Ao to normal.

Naturally, Naruto is too stupid to pull one of these himself. In one filler arc, he, Hinata and Kiba have to deal with impostors copying their every facet. So naturally when trying to identify the real Hinata, rather than asking a baited question like, "Hey, Hinata, how did you defeat Neji during the Chuunin exams?" he inverts the trope, asking, "What is the name of Hinata's father?" — a question any good imposter would study beforehand, but one that Naruto himself didn't know the answer to, making it utterly useless even if the imposter didn't know!

Sakura pulls one of these off against Zetsu, who was impersonating Neji during the current world war. Or rather, Zetsu does it to himself. When Sakura mentions that Tonton (Tsunade's pig) is being looked at for a twisted leg, Zetsu!Neji says that it's better to have injured her leg than her hand, then asks if Tonton can still weave signs. Sakura says yes, but then when Zetsu!Neji comes closer, she pounds him into the ground and tells him that Tonton's a pig.

This is actually quite a clever application by the writers considering that the Zetsus seem to learn a fair amount about the people they impersonate. Neji's team mate is Tenten. It's not such a stretch to think that Zetsu was simply trying to be too clever.

Episode 333: The imposter shows up in front of the real Naruto Uzumaki and declares that he is Naruto Uzumaki. Until Naruto said that he was the real one and the imposter got curbstomped.

Used in the Fullmetal Alchemist manga: Riza Hawkeye and Roy Mustang are hunting down the shapeshifting Envy and get separated; when they meet up again, they exchange a few words, then start off looking for Envy... until Hawkeye puts her gun to Mustang's head. This leads to a universal "oh crap" from the fanbase, until...

Done heartbreakingly in Karin (with a bottle of Tabasco sauce) towards the end of the manga, to determine if the title character's sister has matured to the point where scheduling differences now leave her without any daywalking family. Adult vampires, you see, have no sense of taste.

In Guyver, protagonist Sho is handcuffed to love interest Mizuki so he can't bio-boost without blasting the broad to bloody bits. Hearing half a warning that she might not be who she appears to be, Sho laments that this had to happen right after Mizuki's birthday. She agrees, and her cover is blown because Sho knows her birthday is later in the year.

Love of Fresh Pretty Cure! bluffs an impostor of her mother by switching her and Setsuna's presents and thanking her for the wrong one. Since Love is an Idiot Hero, everybody else had already figured out that the Ayumi living with them was a fake already, but it's the thought that counts.

In Digimon Xros Wars, episode 39, Kiriha suddenly remembers to return a Digimemory he borrowed from Taiki, and Taiki agrees. Except that the borrowing never happened, and Kiriha hands over a small explosive device that ruins Splashmon's impersonation of Taiki.

In Love Hina, Keitaro lies about being a student at Tokyo U, so Naru asks him about the miso-boiled lobster they serve in the cafeteria. Keitaro babbles on for a bit about how it's his favourite food that he can't start the day without, before Naru tells him that there is no such thing as a miso-boiled lobster.

During an attempt to find an enemy Stand user in JoJo's Bizarre Adventure: Stardust Crusaders, Jotaro accuses his suspect of being one, adding that Stand users have blood vessels stand out on their nose when they inhale cigarette smoke. All of his allies reach for their noses... as does the suspect. Then Jotaro adds that he was bluffing, and his suspect drops the innocent act.

Happens in K-On!: Ui has disguised herself, rather convincingly as Yui until she slips polite speech which starts to undo her cover. She tries to deny it but Azusa demands Ui call her by her nickname.

Comic Books

In the Team 7/Weapon X crossover, the two squads meet in an underground base they were both tasked with blowing up. At gunpoint, they ask each other sports questions to find out if they are Soviets. Amusingly, Wolverine (a Canadian) asks a hockey question, which would probably be more easily answered by a Russian than an American.

In Doctor Strange: The Oath, Doctor Strange encounters a demonic entity who tries to convince Strange that he is facing one of his most powerful foes, Dormammu. Strange, suspicious of Dormammu's sudden arrival, asks him, "So where is Umar, your rapscallion of a brother?" When Dormammu answers, "He is none of your concern," Strange has his answer; Umar is Dormammu's sister.

In Ronin, Peter's suspicions of "Taggart" not being what he seems are confirmed when he doesn't react when Peter claims that his wife Casey accompanied the two on a trip, when she did not. And when Virgo doesn't react either, he knows she's in on it too.

The Dark Lords of Nerima: When Ekim takes control of Ranma's body, with the intention of attacking Sailor Mercury, she intercepts him and, suspicious of his behavior, asks why he'd want to talk to her since she was the one who destroyed the "summoning artifact". Ekim responds that he began to respect her after that, which confirms her suspicion that it's someone else, since Ranma would know it was Sailor Moon who destroyed it.

Stars From Home: Scott uses this when he believes Raven is impersonating Alex; he is already convinced, but tries to prove it to Charles by having Alex describe the day Scott was born. It works. Alex appears several years older due to experiments keeping Scott young. So Alex couldn't remember the day Scott was born—because it happened before Alex himself was born.

Film

The quote at the top of the page from Terminator 2: Judgment Day. The T-800 asks John Connor's foster mother a question about the family dog but intentionally gives the wrong name to see if she's actually the shapeshifting T-1000, and she is. The foster mother doesn't react to his getting the dog's name wrong, thus exposing itself to the T-800. There is a deleted scene where the T-1000 is shown afterwards holding a bloody dog collar, seeing the name on it and realizing that his target knows that he is there and will be avoiding the house.

In Live Free or Die Hard, John McClane mentions a police code to the Big Bad's girlfriend, who is disguised as a police dispatcher. She says that the police had to dispatch all units in regards to the code. McClane coolly responds, "Dispatch all units for the naked people running around?"

Darkman: The villain comments to the title hero, while the hero is in disguise, that he would hate for his (the person who Darkman is impersonating) wife and kids to miss out on such a "great role model." When Darkman answers that they do look up to him, the villain casually notes that he doesn't have any kids, and nailguns his hand to the wall.

Darkman II: The Return of Durant: Durant (the villain) suspects that Darkman is masquerading as Ivan, and to make sure he makes a comment about not having to leave someone's body behind in Saskatoon. He was refering to an earlier conversation, where he's talking to the woman in question in Ivan's presence and states that they'll be burying her in Saskatchewan.

From Dave, where Dave has ben hired to stand in for the President after a stroke renders him comatose.

Ellen (The President's Wife): Reminds me of when you were in the state legislature. Dave: Yeah... me too. Ellen: You weren't in the state legislature. (stands up and offers her hand) Hi, I'm Ellen Mitchell. Who are you?

The main villain of The Master of Disguise uses this in one of the final scenes to uncover the identity of the disguised hero, who had given himself away by forgetting to change his shoes.

In The Spiderwick Chronicles movie, the main character's father seems to appear and he (the kid) asks his dad what it was he wanted to tell him. He's actually the villain, and the kid finds this out because his father was supposed to tell him they (the parents) were getting a divorce.

Clouseau: What is your code name? Dreyfus: I don't have a code name! I never had a code name, lunatic! Clouseau: I understand sir, but you see, only the real Inspector Dreyfus would know he did not have a code name.

T.K.: That first time we met at the bookstore, did you ever imagine we'd end up in a mess like this? Yulaw: Even if I had known, I still would have done it. T.K.:(turns gun on Yulaw) It wasn't a bookstore.

In Invasion U.S.A. (1952), several Soviet paratroopers approach Washington D.C. disguised in U.S. Army uniforms, in the latest phase of the titular invasion. They're stopped by a guard who notices that the troops are "apparently" from Chicago. The guard asks the leader of the troops if he ever saw the Cubs play. The confused leader says, "Cubs? A cub is a small animal, a bear."

In The Negotiator, Sabian is trying to talk down negotiator-turned-hostage-taker Danny Roman. When Roman demands to talk to a confidential informant that can't be located, Sabian reasons that Roman doesn't know the guy either. He substitutes an impostor but is caught when Roman slips in a reference to the impostor's time playing ball for Colorado State and the impostor fails to challenge it despite having Arizona State in his personnel file.

Eyes Wide Shut: This is how Bill is called out during the orgy sequence. He's asked for the house password in addition to the admittance password, which he says he forgot. Later on, he's told that there was no house password.

In Ronin, Sean Bean's Spence character is revealed to be a wannabee fraud of a spy when he is asked, by Sam (Robert De Niro), what the color of the boathouse at Hereford is (the main British SAS base), and is unable to provide an answer. After a shamed Spence shuffles away, Sam is asked what the color of the boathouse actually is, and he replies, "Hell if I know."

In Alone With Her, when the protagonist, the girl he's secretly spying on/manipulating, and her best friend are having lunch, the best friend asks him if he'd been to a particular fashion district in Seattle (since he claims to be from Seattle). He says yes, and once he's out of the room, the best friend reveals that she made the fashion district up.

In the Jet Li film Black Mask one of the Super Soldier villains has infiltrated the police and gotten into the unit led by Li's best friend. Late in the movie Li's friend begins to notice the suspicious behavior from the infiltrator, and begins casually asking the infiltrator a few questions, like how long he's been on the force (about a year) and which department he was in before transferring into this unit. In response to these answers, Li's friends says that means the guy must have served with Captain Chan, and talks about how nice a guy Chan is. When the infiltrator agrees with this he's immediately shot: "Chan died four years ago, and he was a real prick!"

In There Will Be Blood, Plainview recalls events in his hometown to test whether his half-brother really is who he says he is.

Stalag 17: The Mole tips off suspicious cabinmates by mentioning that he was eating dinner when the attack on Pearl Harbor occurred. While it was noon in the Eastern time zone when the attack happened, it was dinnertime in Germany.

Variation in Men in Black: Agent K exposes an alien posting as a Mexican immigrant by saying insulting and threatening things in Spanish, but in a cheery tone of voice, to see if he reacted appropriately.

In the Gene Hackman film Narrow Margin, Hackman's character tells a pair of "RCMP officers" that he might have the guys who've been pursuing him and his witness all over a train "on a 374". They agree, which tips him off to their being fake. 374 is "indecent exposure".

The Disney Channel Original Movie The Famous Jett Jackson has the titular character swap places with his secret agent Show Within a Show character Silverstone. Meanwhile, the show Silverstone has a new Big Bad (Michael Ironside) with the ability to disguise himself as any person, and Jett (the actor) has to figure out a way to defeat him, while Silverstone has to pretend to be Jett and deal with Real Life problems in a small Southern town. Suspecting that the Big Bad has infiltrated the spy agency, Jett demands Silverstone's mentor sing him the song he sang Silverstone as a baby. While the mentor sings "The Itsy Bitsy Spider", Silverstone's partner starts slowly moving towards the dimensional key. Jett catches her hand and has the mentor invoke this trope. The question is about the name of the plant he gave her for her Birthday. She replies that she doesn't have one name for it. Of course, there is no plant, and she is the Big Bad in disguise.

In A Series of Unfortunate Events, Uncle Monty exposes Count Olaf (pretending to be a herpetologist named Stefano) as an imposter by asking him to milk Petunia the snake. "Stefano" started looking for udders.

In Diamonds Are Forever, Mr. Wint and Mr. Kidd pretend to be room service and serve Bond and Tiffany diner. After they serve the drinks, Bond remarks he would have liked to drink a claret. Mr. Wint apologizes and says they ran out, then Bond points out the drink they served was a claret.

In Midnight (1939), when Eve poses an an Hungarian royal blood, Georges is onto her and asks if the Budapest subway has been finished yet. She replies that the streets are still torn up. However, as George later reveals, the metro was already finished 50 years ago.

Gamebooks

In the third book of the Lone Wolf series, The Caverns of Kalte, Lone Wolf meets a prisoner in the enemy's fortress, who pretends to be a merchant from Ragadorn, but is in fact a Helghast shapeshifter sent by the Darklords. The game allows asking him a few questions about the city of Ragadorn (visited by Lone Wolf in his earlier quest), and the monster gets the answers wrong. The text never points out whether he is right or not, however: it is up to the player to remember what are the correct answers from the previous book.

In Harry Potter and the Half-Blood Prince, the Ministry advises people to ask this kind of question to make sure a Death Eater isn't impersonating your friend. Harry quickly figures out for himself that when magical compulsion is one of the favorite tools of the bad guys, this sort of thing is the barest of bare-bones contingencies.

It's also inverted: Arthur Weasley comes home from the Ministry and passes Molly's challenge at the door. When she goes to open it, he grabs it and pulls the door shut again so he can challenge her. Afterwards, Molly comments that it's silly, since anyone impersonating Arthur could easily torture the question and response out of him. He agrees with her, but says that they should do it to set an example.

In Harry Potter and the Deathly Hallows, members of the Order of the Phoenix start doing this to each other. Guess they decided the idea wasn't so useless after all. There is the slight variant that they don't agree on what questions to ask beforehand, instead just asking about random moments in their past, making the system more secure.

In Robert A. Heinlein's Double Star, a disguised actor impersonating a politician meets with the Emperor of the Solar System. The Emperor insists that he play with his toy trains, which the actor dutifully does. The Emperor then asks him who he really is, because all the past times he had met with the politician and asked him to play with the trains the politician had refused and teased him about having such a childish hobby — it was a sort of game between them. It was an interesting play on this trope, as the actor's impersonation was so flawless that the Emperor hadn't really been all that suspicious until that point.

In The Savage Damsel and the Dwarf, the title characters are staying with a group of knights, and the dwarf mentions that he used to serve Sir Gaheris. One of the knights asks casually if Sir Gaheris is still as skilled a swordsman as ever. The dwarf who is actually Sir Gaheris under an enchantress' curse passes the test when he responds that the knight must be thinking of someone else, since Sir Gaheris is a notoriously abysmal swordsman.

In one of the Animorphs books, when David acquires (gains the ability to morph into) Marco, Rachel taunts the real Marco with "You know you're a toad, right?" and Cassie asks him to describe how it felt when they morphed trout. They know it's Marco because he answers sarcastically ("Kiss me and I'll become a prince," and "The cracker crumb coating chafed," respectively).

Marco does beg for them to not try this, because he's terrified that he'll miss a punchline, and Rachel will eat him before he has a chance to explain. (Although, that could be sarcasm, too...)

In another book, a Controller says the word "Andalite!" loudly to a person he suspects to be an "Andalite bandit" in human morph. In reality, he's as close to being right as you can be, as the person in question is Cassie in Rachel morph. But he's satisfied when, without missing a beat, Cassie/Rachel immediately replies as if he had just said the words "and a light".

Marco also does this after his dad discovers Z-space, trying to see if his dad's a controller by pointing out that the trip his dad wants to take would mean they'd be gone more than three days, the amount of time a Yeerk can go between feedings.

In one of the Ranger's Apprentice books, Will is in disguise as a minstrel. The lord of the castle he's visiting asks if his instrument was made by the master luthier Gilperon, and Will says no. Later the lord informs him that the luthier's name is actually Gilet, which a real musician would have known.

In John Barnes's One for the Morning Glory, the Duke challenges Sir John to name Calliope's birthmark on her thigh. Sir John sputters. Given that with Sir John's reputation, any imposter would have improvised because of course Sir John would have known.

Used in Dan Abnett's third Eisenhorn book, Hereticus. Eisenhorn spots an imposter posing as a trusted member of his retinue by saying their situation reminded him of the tight spot they'd been in fighting Beldame Sadia on Eechan. The imposter agrees, alerting Eisenhorn (and any particularly astute readers) to the trick — they'd actually fought Sadia on Lethe Eleven.

Subverted twice and played straight once in Isaac Asimov's short story "Little Lost Robot". Robots in this universe are normally Three-Laws Compliant, but a few special robots have been made with a modified First Law: while they still cannot harm a human being, they have no problem letting human beings be harmed by outside forces. The heroine wants to find one such robot who has hidden himself in a roomful of normal robots. Three attempts are made to invoke this trope. The lost robot foils the first because, while it doesn't have to rescue a human in danger, it can choose to do so. So they try to put the robot in a situation where trying to rescue a human would (as far as it knows) destroy it (prohibited by the Third Law unless trumped by the First or Second). Indeed, the robot does not try to rescue the human — but has cleverly convinced the other robots not to try either (they'd be destroyed before succeeding, and the First Law doesn't require futile attempts). In the third attempt, the heroine puts the robot in the first situation again — but the other robots think it's the second, and stay still; the only reason the robot realized it wasn't was that he had some training with radiation and could tell the difference between heat and gamma rays.

It also shows up in Arthur Conan Doyle's Sherlock Holmes story The Adventure of the Three Garridebs. When a man claiming to be an American lawyer recently arrived in London calls on Holmes, Sherlock first asks whether the American had placed an ad in the "agony columns" and is assured that he did, then when the 'American' says he's from Kansas, Holmes mentions an old correspondent of his, Dr Lysander Starr, who was "mayor of Topeka in 1890." The 'American' assures him that Dr Starr's memory is still honored in Kansas. After he's left, Holmes assures Watson that he's not what he claims - there was no ad in the agony columns and "Dr Lysander Starr" is completely fictional.

Also shows up in The Lost World (1912), when Malone is trying to gain Professor Challenger's trust by pretending to be a fellow scientist, Challenger quizzes him on various scientific terms, all of which Malone claims to be familiar with. Challenger then informs him that he had been speaking gibberish and tackles him out the door.

In one of Robert Asprin's Phule's Company novels, a Space Legion soldier trying to prove his identity is asked "Who led the Galactic League in free flies last season?" Not only can he not come up with the player's name, he misidentifies the sport—and his comrades conclude that it's really him, because he's known to be completely ignorant about sports.

In Haunted, one of the Women of the Otherworld series, Lucas asks "Jaime" if she wants Indian food, confirming Eve's claim that she's been possessed by a demon ghost.

Appears in The Light Bearer, a historical-fiction story about the Roman conquest of Germania. Germanic chief Baldemar reveals an imposter to be a foreign spy by asking him if a famous local woman has recovered from an illness, to which he replies that she has — she actually died the previous year.

In White Cat, Cassel casually asks his brother Barron if he remembers certain incidents from their childhood, and Barron says he does... except the incidents are things Cassel made up, or that happened to someone else. In this case, though, Barron isn't an impostor; he's suffering from memory loss and trying to cover it up because he's a memory worker suffering the magical backlash from repeatedly altering Cassel's memories.

This is how, in an early arc of Perry Rhodan, Atlan discovers that the eponymous protagonist has been replaced by a doppleganger — specifically, his first son who has undergone a Face–Heel Turn. The impostor has most of the original's current knowledge due to his allies telepathically interrogating the former before setting the plot into motion, but Rhodan managed to slip in just enough misinformation about his initial clashes with Atlan for the latter to catch on once the subject comes up. (In their first duel in that museum on Venus, they fought with broadswords, not smallswords, and the imposter then failing to recognize a silly little rhyme that had special meaning for them both after a long, wearying chase on the planet Hellgate cinched it.)

In a Nancy Drew book, Nancy has become suspicious of a young man claiming to be the long-lost son of the wealthiest man in town. (The man was presumed dead in an avalanche during a trip to Switzerland but has returned several years later, claiming to have been recuperating in a hospital all this time). While initially charming everyone, he still makes several mistakes — buying his housekeeper a chocolate cake for her birthday when he should know that she's allergic, as she once had a severe reaction in front of him. Nancy finally trips him up by gushing about his 18th birthday party (the last one he had before vanishing), mentioning how cool his "giant purple and white football cake" was. The man enthusiastically agrees — until Nancy coldly informs that that's NOT the kind of cake that was served.

In Kurt Steel's The Imposter, the president of an aircraft company, after discovering the dead body of a double who was sent to impersonate him in a Nazi plot but ran afoul of an entirely separate Nazi plot to assassinate said president, decided to pretend to be the double in an attempt to flush out both sets of enemy agents, but was revealed when one of the dead man's more suspicious associates made some comments about things which had never happened.

It's not pointed out, but longtime readers might also catch the fact that the vampire had exclaimed "lawks!", a stereotypical old-lady cry which the elder witches only resort to when they're pretending to be harmless.

In Vladimir Vasilyev's The Treasure of the Kapitana, an Albionian (British) captain is seeking to hire a Tauridan (Crimean) pilot to help him sail the treacherous waters of the Euxine (Black) Sea. While the local pilots (called "shtarkhs") use more magic than learning to navigate the sea, Ralph also has a piloting degree from the Southampton Naval Academy. He shows his diploma to the captain, who immediately asks how his good friend the chancellor of the academy is doing, seemingly forgetting his name. Ralph helpfully supplies the name and, when the captain asks how the chancellor's wooden leg is feeling, calmly corrects him that, when Ralph last saw the chancellor, he had two good legs but only one eye.

The Reynard Cycle : Reynard enters into one of these with a shapeshifter who has done its research during Reynard the Fox. The one thing it fails to mimic is Reynard's complete contempt for authority, even in the face of death.

In Kir Bulychev's Alice, Girl from the Future series it happens very often, considering that Alice's Arch-Enemy is a shapeshifter. It's taken Up to Eleven in The Jewelry Box of the Pirate's Mother: Alice encounters someone looking like her friend Rrrr, only she had just helped the latter flee, bandaged and bleeding. Pretending to be happy, she reminds the false Rrrr that she had to come to Brastak (his planet) from Earth via another planet (while in reality she flew straight there from the planet Penelope), tells him that on Earth it's raining mushrooms, and asks him if he remembers how they met on Pataliputra and played in the snow (that planet has tropical climate even in the polar regions). When he doesn't react to any of these absurdities, she is left with no doubt that it's an impostor.

Live-Action TV

In the The X-Files episode "Three of a Kind", this is actually used against the Lone Gunmen when Byers is attempting to pass himself off as a defense contractor. One of the other players at the poker table asks him a question: Langley, who has been providing research and info to support Byers' masquerade, comes up empty and tells Byers to fold. Byers, unfortunately, is feeling too bold for his own good, and exposes himself with a blatant lie.

In "Balance of Power", Lister suspects that the Kochanski that visits him during his chefs exam is a fake when she uses the phrase 'up-up-up the ziggurat, lickety split' - something Rimmer has said before onscreen. To test 'her', he brings up them having had sex behind the bins on the snooker, which never happened, and causes Rimmer to blurt out that Lister never told him that.

In "Psirens", to differentiate between Lister and a shape-shifting, brain-eating Psiren, the rest of the crew got them each to play the guitar. Lister incorrectly believed himself a guitar god, so the Psiren played excellently. The crew then knew which one to blast. Although after hearing how the real Lister plays, they wanted to shoot him too.

Cat: Little survival tip, bud. Never play your guitar in front of a man with a loaded gun.

In "The Arsenal of Freedom", a simulacrum of a Starfleet captain unquestioningly accepts Riker's claim that his ship is called Lollipop ("It's a good ship").

Likewise, in "Allegiance", Picard mentions a recent, still-classified incident in front of a fake Starfleet cadet, knowing that a real one would have no way of recognizing the comment as anything but a meaningless name.

In "Conspiracy," an old friend of Picard's does this to Picard because of alien parasites taking over the minds of Starfleet officers, which is explained when Picard asks his old friend what the hell he's talking about.

Star Trek: Deep Space Nine: In the episode "Inquisition", while Bashir already suspects that things aren't what they seem, he proves it to himself and his captors when he asks what happened to O'Brien's shoulder, previously injured playing racquetball. O'Brien says it got better; Bashir then says it wasn't dislocated during a racquetball game, but kayaking. Holodeck room appears, Bashir's interrogator congratulates him on seeing through the illusion.

Star Trek: Voyager: In "Renaissance Man", Chakotay makes up an incident he claims Janeway told him about. When "Janeway" claims the current crisis has nothing to do with that past one, Chakotay knows that she's a fake. (It was the Doctor being forced to act as The Mole.)

In the pilot for the original series, Kelly Garrett (Jaclyn Smith) was masquerading as a long-lost heiress. She met up with Aram Kolegian (Tommy Lee Jones), who had known the heiress before her disappearance. He casually mentioned several things to her about their past which she agreed with. After she left, he said to himself that he didn't know who she was, but she sure wasn't the heiress because the things he had said were lies.

Subverted earlier in the episode, when an old friend of the family tries to bluff Kelly with stories of her (well, the girl she's pretending to be) childhood litered with incorrect details. Kelly, however, corrects each mistake and calls him out on what he's doing rather quickly.

Episode "The Schizoid Man": After a Village agent surgically altered to look like #6 is killed, #6 attempts to masquerade as the agent to escape. Unfortunately, he talks too much and makes several mistakes, causing #2 to become suspicious. #2 mentions someone named Susan saying something "only a month ago": #6 doesn't react. He asks #6 to "give Susan my regards" and #6 agrees. Later, after #6's escape has been foiled, #2 tells him that Susan died a year ago.

And depending on which episode order you prefer, there's also #6's reaction to #2's mention of "the General" as if he's talking about a person; another episode is about a supercomputer by that name.

Martha uses this on her roommate Jenny in the episode "Human Nature". As it turns out, Jenny has been possessed by an alien lifeform; the alien's responses to Martha's conversation confirm that not only is she not really Jenny, she's not really human.

Martha: Would you like some tea? Jenny: Yes, thanks. Martha: I could put a nice bit of gravy in the pot. And some mutton. Or sardines and jam, how about that? Jenny: I like the sound of that. Martha: Right. Hold on a tick. (discreetly flees)

Also used by the Doctor to find out the Martha clone.

In "The Android Invasion" with Tom Baker, the Doctor realizes he's dealing with a Sarah Jane android when she accepts some ginger beer, the real Sarah Jane having told him earlier that she can't stand the stuff.

In the eponymous final episode of The Keys of Marinus, Ian Chesterton notices that "Arbitan" (actually Yartek, the leader of the Voord, who killed him at the end of the first episode of the serial) is behaving very suspiciously, including not seeming to recognize Altos, who he sent to retrieve the keys before the Doctor and Companions, so he gives him a fake micro-key that they also acquired on their travels instead of the real one — the real Arbitan created the keys and would be able to spot the slight flaw that distinguishes it from the real ones, but an impostor wouldn't know the difference.

In an episode of Xena: Warrior Princess, Xena identifies a supposed Spartan deserter as a Persian spy by asking him if he is eager to see the waterfall in his home town again. Of course, there is no waterfall.

In The Wire, Chris and Snoop find out which drug dealers are from New York and trying to muscle in on their territory by asking things only someone from Baltimore would know. Unfortunately, Snoop isn't that knowledgeable of local pop culture herself, and after she almost kills someone who gives a correct answer, Chris decides that he should handle asking the questions.

In an early episode, this was used to determine whether an elderly alien really was Daniel as he claimed he was. (He was)

Jack: What color dress was your sister wearing when I took her out last night? Daniel-in-Ma'chello-body: I don't have a sister, and if I did, I'd never let her go out with you.

Played with in "1969", when the team has traveled back in time and are assumed to be spies. Not trusting their American accents, the interrogator asks Daniel, in Russian, if they are spies. Daniel answers "no", but instinctively switches to Russian as well. O'Neill is rightly annoyed.

Stargate Atlantis: In the season 5 premiere: Sheppard does this to the people coming to dig him and Ronon out from the rubble of Michael's collapsed base. First he asks if "Harris" is there, and when someone replies in the affirmative, Ronon remembers that Harris is on leave. Then Sheppard offers to buy the rescuers drinks when they get back, asking one if he prefers Duff Beer or Oprah Ale. From the rescuer's obliviousness to the fact that those are fictional beverages, Sheppard and Ronon conclude that their "rescuers" are really Michael's half-Wraith mooks.

The Middleman: The Middleman is being possessed by an evil genius. Ida, warned by Wendy, innocently asks if there's anything he needs from her before she goes home to her husband and children. The fake Middleman, not knowing that Ida is an android, doesn't suspect a thing.

Heroes: When Peter is controlling the body of Jesse, one of the Level 5 villains, Knox, his fellow escapee, catches him this way by asking "Jesse" if he can't wait to see his family and friends in Detroit, when Jesse's family is from Vegas and he doesn't have any friends.

One episode of Big Wolf on Campus uses this trope to help the two main protagonists distinguish between who is or isn't possessed by a vengeful ghost out to murder the main hero. When sidekick Merton Dingle is possessed, Tommy Dawkins is able to figure it out after Possessed-Merton fails to remember the secret word that lets them know if he's possessed or not.

In an episode of Farscape where Crichton believes he has returned to Earth, the alien masquerading as his father pulls one of these. In a later episode, when Crichton really has returned to Earth and meets his father, Crichton references that conversation.

In Twin Peaks, Audrey Horne is caught out this way when she fakes her resume at One-Eyed Jack's.

Michael: Gustavo, we talked about this on the phone. I'm giving you eight thousand dollars for a file. Part of what that money buys is privacy. Contact: I don't care what I said on the phone. You don't tell me what I want to know, you don't get this file. Eight thousand, no eight thousand. Michael: The deal I made with Gustavo was for ten thousand dollars, not eight thousand dollars. He was very clear about that number. And we never talked on the phone. You wanna tell me who you are?

Alias: It seemed to happen quite a lot, due to all the spies, moles, and infiltrators, but mostly due to Project Helix, an Applied Phlebotinum that allowed one person to be identical to another. Will Tippin held a gun on Sydney Bristow because he thought her to be an impostor. He asked her what he spilled on his shirt a decade ago before a job interview and she knew. Similarly, Sydney realized Francine had been killed and replaced with a gene-disguised impostor when she accepted a bite of coffee ice cream, which Francine hated.

Michael Knight finds that the villain with Latex Perfection is not Devon by calling him Ishmael, which confuses him. Earlier in the episode, Devon had greeted Knight quoting the beginning of Moby-Dick: "Call me Ishmael".

In another episode, when a girlfriend expresses concern about her father's behavior (he's been kidnapped and replaced with an impostor), Michael chats with him about the Disneyland tickets he had supposedly asked him for. When the man responds enthusiatically, Michael and the girl know he's a fake — they had never made any such plans.

Family Matters: Urkel is the captive of a man impersonating Carl's partner. Carl hears him talking through the door and not giving the standard reply of, "Not if I see you first," when he says, "See you later." Carl baits the kidnapper by sliding money under the door that he doesn't owe him and breaks it down when he comes to get it, then apprehends the felon.

Sanctuary: Will and Helen are among the survivors of a plane crash who are being picked off one by one by a creature that can create visual illusions. They know the creature can make itself appear to be one of the survivors, but they don't know who it is. The creature lures Will out of the plane and takes on his appearance. Helen catches it when, as Will, it offers her a cup of tea and she claims to prefer coffee; the real Will would have known that Helen hates coffee.

In the Poirot episode "Hickory Dickory Dock", one of the students professes to be an expert in Keats. When Poirot quotes some poetry at her she assures him that he certainly knows his Keats. The only problem is that it wasn't a Keats poem.

One episode of the 2009 V series has Erica out James May's girlfriend as an undercover V agent using this method. They were engaging in small talk about (among other things) where she went to college, and Erica deliberately referred to the wrong football team, which exposed the alien when she failed to correct the error.

Kamen Rider Blade had a variation on this in the Hyper Battle Video, where a Trial has impersonated Kazuma, and subsequently Blade. Hajime roots out the Trial by calling out Kazuma's name; after the battle, he explains that the Trial reacted first because of its superhuman reflexes, to which Kazuma responds "That makes me sound kind of slow, doesn't it?"

The Gemini Man: Used by Intersect Agent Sam Casey (also seen in the Mystery Science Theater 3000 episode "Riding With Death," featuring two episodes of the series repackaged as a TV-movie) on Dr. Hale, who is supposed to be in the trailer of the truck Sam is driving, but suspected of being in the helicopter that's been following the truck the entire episode (which he is). Dr. Hale has rewired the intercom in the back of the truck to communicate with a radio unit in the helicopter.

Sam Casey: Sorry about that last bump, Dr. Hale. I hit a hole in the road. Crow: He's mellow but cunning. Abbey:(trapped in the back of the truck) What bump? Sam: I hope it didn't jar you too badly. Dr. Hale: Uh, well it almost knocked my glasses off, but that isn't important. We have to make up that lost time.

In an episode of Lie to Me, Cal and Torres visit a fertility clinic, posing as a married couple looking for an egg donor. Cal asks if what they've been told is possible, namely that his "wife's" infertility is due to an estrogen imbalance caused by the Coriolis effect, and the doctor agrees that it's a definite possibility. Had he been a real doctor, he would have known that the Coriolis effect has nothing to do with medicine.

In an episode, Jessica becomes suspicious of a man's claim of having been in the armed forces. To that end, Jessica asks if he served in X division with her husband Tom. The man readily claims that he did and describes Tom as a fine soldier and one that he admired and respected. Of course, Jessica knows he's lying as her husband's name was NOT Tom, and he served in a different division of the armed forces than the one she named. However, she doesn't confront him with this, nor reveal it to anyone else, knowing the man could easily Hand Wave it as an honest mistake rather than an outright lie.

In another episode, she pulled a similar stunt with a professional chef, asking him about a favorite recipe of hers, claiming it was a pork dish with Bearnaise sauce. This tripped up the chef because the dish in question was actually salmon. The chef was then forced to confess that he did not graduate from cooking school, which tied in with a possible motive for murder at the restaurant where he worked.

A case of bluff the witness is used in The Good Wife episode "Unprepared". Once they realize the witness is the one who committed the crime (he claimed he made a cell phone call in an area with a phone block), they ask if he made the call during the intermission of the recital he was at. He says he did, and they point out that there was no intermission.

A storyline on Third Watch had the cops are searching for a pair of rapists who pose as police officers so that they can pull women over and then assault them. At the episodes end, as the fake cops are menacing a woman, the real cops arrive. The fake cops try to claim that the woman's screams for help are just the raving of someone high on drugs. Already suspicious (they know the woman and know she's not an addict), one of the real cops asks the fakers a question in "cop lingo". When he's unable to answer, they instantly know they've caught the criminals.

Frasier. Roz discovers she's pregnant, and Frasier encourages her to find the father and tell him the news. She claims one morning at Café Nervosa that the father was an architect, and not much else. Later, at Frasier's apartment, she mentions that he was an archaeologist, and Frasier gets her into the kitchen to pull one of these off the bat by asking her how the two met again.

A General Hospital storyline had a woman named Katherine Crawford coming to town, claiming to be friends with the recently deceased Dominique Baldwin and rapidly befriending her widowed husband, Scott after learning that Dominique was dead. However, Scott's friend Lucy was immediately suspicious and began to investigate. Her first discovery, that no one named Charles Crawford had died recently (Katherine was claiming to have been recently widowed herself) was thwarted when Katherine stated that her married name had been Reynolds. But her second attempt proved successful when she was able to present the real Katherine Crawford to Scott. Unfortunately, Scott decided to believe Katherine's lame excuses, leading Lucy to have to make another discovery to prove Katherine's duplicity—upon re-reading the letter than Katherine wrote to Dominique, she realizes that Katherine used her fake name, something that would have been unnecessary if Dominique knew her. Which meant that Katherine ALREADY knew that Dominique was dead before coming to town, and that her intent from day one was to scam Scott out of the money that he'd inherited.

From the same show: Twice, Serial Killer Ryan Chamberlain escaped from prison and took his twin brother's place in Port Charles society so that he could continue to stalk Felicia Jones, who he was obsessed with. In both cases, Kevin managed to alert people by discussing events that Ryan couldn't have known about.

A short-lived spy series in the sixties had the hero pull a Dead Person Impersonation of a wealthy man who'd been killed by Soviets when they mistook him for the spy. The rich man's wife caught on to the imposture fairly quickly, because her husband was a Jerkass, and the agent treated her with courtesy. She tested him by asking if he'd consulted his sister about a certain business dealing. Not having had the chance for a proper briefing about the man he posed as, he said dismissively, "What does she have to do with it?" Of course, "My husband doesn't have a sister." She wound up covering for him anyway.

The crew is trying to decide if their most recent addition is truly a POW or a spy. Hogan tells his men not to ask about Ty Cobb's batting average as that's the first thing a spy would learn. Later on after correctly answering questions on American cities, one of the men asks the spy if he knows anything about Ty Cobb, to which the spy asks "Want to know his batting average?"

In another episode, one of Hogan's crew is trying to infiltrate a meeting of German officers under guise of another visiting officer. One of them, perhaps sensing an impostor, says he had heard that he injured his hand in a hunting accident, and asks him which hand it was: the right or the left? The spy manages to dodge the question by saying: "Thanks to superior German medical techniques, you can't tell which of my hands was injured!"

Averted in season 5 of Lost when Pierre Chang realises that Hurley is probably from the future. Hurley blows his cover when he mistakes a straight question for a bluff.

Chang: What year were you born? Hurley: 1930. Chang: So you're 47 years old? Hurley: Yeah. Chang: And you fought in the Korean war? Hurley: There's no such thing!

Played much less seriously in the pilot of The Chicago Code. Wysocki asks his partner what time the game starts, and Evers tells him 1:20. Wysocki notes that the White Sox have the day off, which blows Evers' cover revealing himself for the traitorous Cubs fan he truly is.

On Fringe, Peter eventually uses this on Fauxlivia, reciting a line of Greek to her that the genuine article would have recognized. Unfortunately he wasn't very subtle about it, and she was waiting in the next room with a gun.

Revenge: Victoria invites the fake Amanda Clarke to tea and serves strawberries. When "Amanda" eats them, Victoria recalls her having had a severe allergic reaction to strawberries as a little girl. "Amanda" claims to have grown out of the allergy, but Victoria now knows she's an impostor because she made up the whole thing.

In the Supernatural episode "The Great Escapist", Properly Paranoid Kevin Tran grows suspicious when the apparent Winchester brothers forget the secret knock and sends them to get him takeout barbecue. When they obey with proper deference to a Prophet of the Lord, Kevin knows that they're Crowley's Mooks in disguise and sends them into a trap.

Double subverted in the much earlier episode "Skin". Sam suspects that a shapeshifter they're chasing is posing as Dean. He asks a supposedly casual question that's pretty obviously a test. The shapeshifter has access to Dean's memories and answers correctly, so Sam tosses him the car keys. However, the question was a red herring; the real test was the keys, which "Dean" caught with his left hand despite the real Dean having an injury to the left shoulder.

In an episode of Sliders, Quinn impersonates his double until the double's friend and villain of the week successfully bluffs him. Quinn accepts the man's invitation to go sailing; unfortunately for him, he didn't know his double was terrified of water.

In one episode of Misfits, Jess exposes an impostor by casually asking the character in question about the new car he doesn't have.

In Outlander, Claire tries to bluff Jack Randall into releasing her by claiming that she also works for his patron, the Duke of Sandringham. She tries to remain vague when Randall asks her if she met the Duchess, saying that she got her orders by letter, but she's still foiled because she doesn't know that the Duke never married.

In the season 2 episode Face My Enemy, Agent 33 disguises herself as agent May to lure Coulson into a trap. When Coulson gets suspicious, he casually asks 'May' if they could finally get that cup of coffee they discussed years earlier when this mission is over. When May agrees, Coulson knows enough; the real May hates coffee.

In Love in the Face of HYDRA this happens again, this time Agent 33 vs Talbot. To be fair, Talbot realizes very quickly and notifies Coulson "The nanomask is in play", and assembles all female staff workers, even telling his security not to let anyone disturb him, even if it is him. He even knows a lot about his staff, knowing which lines to say and how they should respond. However, he fails to realize that 33 can adopt either gender; or believed they were restricted to one gender, as when he himself was impersonated, it was by a man whom he knows is in custody.

In a recent episode of NCIS: Los Angeles, Sam and Callen are kidnapped and trapped in a warehouse. They escape and shortly after run into a man claiming to be an abducted NSA agent. Sam secretly decides to test him by asking him which way he exited NSA HQ the day before. The man answers with a route that Sam knows is blocked by construction, revealing that he's an impostor. Sam lets Callen know via Trouble Entendre, and they secretly turn the tables on him.

In an episode of Painkiller Jane, Jane is set up by a wild scheme to give away the location of her team's secret headquarters. Part of the plot has her "rescued" by a shapeshifter posing as her best friend, Maureen. When Jane notices the woman doesn't have a recently applied tattoo, she talks of how she forgives Maureen for sleeping with a classmate in college. Later, after the shapeshifted is captured, they talk as it turns out the guy was the class geek and thus Jane knew it wasn't the real Maureen.

In Oz, Adebisi asks undercover cop John Basil about various criminals "Desmond Mobay" should know if his identity is genuine. He slips in a name that Basil doesn't recognize, and Basil either knows he's bluffing or suspects he might be.

Desmond Mobay: I never heard of that guy.

Simon Adebisi: That's because I made him up.

Podcasts

Dice Funk: Rinaldo does this to the fake lord's son by referring to a non-existent deceased aunt.

Radio

In the Adventures in Odyssey episode "Sheep's Clothing", a suspicious pastor asks "Paula Jarvis" (who has already slipped a few times) about the annual blueberry festival from where she supposedly grew up. He doesn't mention that they actually grow strawberries there...

Paul Temple and his wife Steve sometimes use this to subtly reveal impostors.

In "Paul Temple and the Gilbert Case", concerned for the safety of his wife, they agree on an arbitrary question/answer which only they will know, and which she can use to challenge any telephone caller claiming to be him. When Steve first uses the question, the caller really is Paul (although there's a cliffhanger before he answers, which initially makes it seem like he's an impostor); the second time is a subversion, but on a subsequent occasion, in "Paul Temple and the Conrad Case", it's successful in revealing an impostor.

Also in "The Gilbert Case", Steve herself is bluffed by the owner of a nightclub who mentions a "lifelong friend" of the person whose membership has allowed Paul and Steve into the club (and who is actually an undercover detective). Steve says that she knows the friend well, but finds out soon after that he doesn't exist. Needless to say, she has a mild Oh Crap! moment when she realises she's been had, although it turns out that the owner knows about the detective anyway.

In a second example from "The Conrad Case", Temple speaks to Elliot France, another author, over the telephone, and congratulates him on the success of his book "Zero is Tomorrow" — "France" thanks him, but the title is actually that of Temple's next, as yet unpublished, novel.

Myths & Religion

A variant occurs in The Odyssey: Penelope uses this to see whether the man claiming to be Odysseus after 20 years really is her husband. She orders their bed to be prepared and placed outside the bedroom; Odysseus protests that this couldn't be done as he carved the bedpost himself out of a living olive tree still rooted in the ground, thus proving his identity. Making this one Older Than Feudalism.

Also, the Gileadite trap for Ephraimite spies in Judges 12. The Ephraimites were unable to pronounce "sh" properly, so the Gileadites used the word "shibboleth" as a password — if you couldn't make the sound correctly, and rendered the word "sibboleth", it was definitely not your lucky day...

In Professor Layton and the Curious Village, the protagonists get suspicious about Inspector Chelmey when they find a newspaper article mentioning the man's love for sweets when previously he had violently objected to being served tea and cakes. They question him about this and mention his wife's name... only they give the wrong name, and he proceeds to parrot the mistake, exposing himself as an impostor.

Played with in Fallout 2 by Renesco the Rocketman when you're looking for parts. After giving the password, you're asked for the second password - your only response is to cuss out the foreman for not giving you the second password. Renesco then says to relax, that there was no second password. Humorously, if you leave this quest on the backburner for too long, you can forget the first password too...

The Wanderer: Marcus says... shit... Renesco: "Really? I'm sure he didn't send you all the way down here to say "shit".

An interesting case in Dragon Quest VI. The Hero enters Somnia Castle in the other world after discovering you look exactly like the missing prince. The chancellor, having heard that someone in town purchased noble clothes like what the Hero is wearing and he asks the name of your long dead sister. All of the available choices are wrong. Then again, it turns out that the Hero is the Prince of that world's Somnia...sort of.

A body-snatcher variant appears in Mega Man Battle Network 4: Blue Moon, in which Lan got suspicious when Mega Man tells him to forfeit the tournament. So Lan decided to quiz him, and the player selects the answers. One of the questions is about what is Lan's favorite food, and none of the choices given are correct.note For reference, it's curry. This allows Lan to determine that Junk Man is controlling Mega Man's body.

Not really a case of an imposter, but in Tales of Symphonia, Lloyd suspects that something's not right with Colette, and tricks her into revealing that she's lost the ability to feel anything by bluffing her about how hot (or cold) the cup of coffee he brought her is.

Visual Novels

Late in Tsukihime, in a moment of uncharacteristic brilliance, Shiki inserts an incorrect detail into the story of how he received the ribbon he promised to return to its owner when he left the Tohno mansion. Hisui does not spot the detail, however, which lets Shiki figure out the Twin Switch, and that the twin who watched him from the window is actually the Stepford Smiler Kohaku. Since the reader already knows the truth from one of the previous routes, it is not a big surprise, but it does alter how the story unfolds after that point.

Web Comics

Casper uses this on "Komi" in Darken.It works, but Casper finds himself in a less than ideal situation as a result.

Agatha uses this tactic to sound out whether Othar is the real deal. (He is.)

Later, the Heterodyne's seneschal Carson von Mekkhan uses a variant on the same trick to test whether Agatha really has a Heterodyne heritage or not. (She does, but her performance fails to entirely convince him.) Eventually Agatha got tired of the questions and started telling him things that only a real Heterodyne should know, which caused him to end the interview and move on to the next stage of confirming her heritage.

In General Protection Fault, Nick uses this to confirm whether he's dealing with the real Ki or not shortly after he's been kidnapped into what turns out to be the Negaverse. Nega-Ki gets the name of a place in an unfinished novel of Ki's wrong, which proves to Nick she's not his Ki.

Madblood uses this to prove that the disguised Dave isn't really him from the future.

Dave: Yes, Lupin of the past, I've long ago solved all your petty problems. Madblood: Ah, good! You can tell me how to correct the degradation of 500th-generation molecular cascade patterns on my liguid-crystal microcircuitry! (beat)Dave: Should I save us some time and admit I'm not actually you? Madblood: That'll do nicely. I have no idea what I just said anyway.

Later on, Helen immediately spots Madblood (disguised as Dave) as an impostor, and decides to mess with his head by pretending she and Dave had an affair, which Madblood is forced to play along with.

In Visseria, done by a nameless guard to Jack after he casually mentions a nearby residence that he's supposedly leading the guard to.

In Defenders of Stan, Butt Monkey Stan has a deathray pointed at two guys. One is his jerkass brother, Ted, and the other is his brother's evil robot clone. Stan says, "I love you, Ted." The robot clone says that he loves him too while his brother laughs and calls him gay.

In Worm, the fact of Regent's People Puppets power leads to Weld subjecting Shadow Stalker to one when she shows up with several members of the Undersiders in custody.

Not Always Right's main archive has this lovely story, where a scammer tries to claim they weren't delivered any of the items they ordered. The cashier follows along until calling them out at the end.

Western Animation

Hilariously overblown in Fantastic Four: World's Greatest Heroes "My Neighbor Was A Skrull" when shapeshifting aliens are posing as every single one of the heroes' neighbors and acquaintances. Reed Richards starts asking questions like "Do you remember when we first met? Was it... five hundred years ago? On the moon? Remember, you flew up there in your bathtub?" and "I always loved your wings, Mrs. Smith. They're so white and fluffy. Would you show them to me, please?"

In The Real Ghostbusters, Egon bluffed a Janine imposter by referring to his mother as his Aunt Helga. The real Janine would recognise Egon's mother because they've met before.

In Transformers Prime, Bulkhead thinks there is something off about his friend Wheeljack. He asks him about a certain battle. His friend recites what he did perfectly, except he says that Bulkhead was there, when he was already with Optimus.

In the Regular Show Episode Temp Check, a temp that Rigby hires turns out to be a shapeshifter that gradually changes until it's impossible to to distinguish between the two of them. The attempt to get the impostor to expose himself by asking questions fails, so Mordecai offers the winner of the challenge a hug. "Rigby" takes it, which outs him as the impostor (since, earlier in the episode, it's shown that Mordecai and Rigby would never hug one another.)

Sonic SatAM had Sonic bluff a robot imposter of Sally with a long and rather complicated handshake that they tended to use. However, he changed the last part from a thumbs-up to a thumbs-down. When Sally followed along and didn't correct him, Sonic knew she was an impostor.

In the Hub's Pound Puppies, Squirt trades places with pampered house pet Cuddlesworth in "The Prince and the Pupper", and meets Cuddlesworth's fellow pet, a Persian cat named Madame Pickypuss. Pickypuss manages to confirm that Squirt is an impostor when he accepts a treat that she knows her friend Cuddlesworth hates.

In Tuff Puppy, The Chameleon got into a tussle with Dudley, while disguised as Dudley, Kitty was able to tell who was the real Dudley by getting one of them to spell Dudley's name, the Chameleon got it right and she blasted him. The real Dudley can't spell his own name, let alone write it down.

Real Life

In World War II: A variation for those on watch both used and inverted this system: The guard would state "The Land of the Free," to which an American would reply "And the Home of the Brave." Then the guard would state "The Terror of Flight," to which a German would reply as "And the Gloom of the Grave"... Every American soldier would know the first verse of their national anthem, but only a spy trying too hard to pass as one would know the third verse.

El Al security guards ask similar questions of the airline's passengers. For example they might ask if the passenger saw a sporting event that didn't actually happen. If they say "yes" it's a good sign they're hiding something.

To shortstop this trope, India-based workers who do tech support for American companies will sometimes have current weather information or sports information up for whatever American city they claim to be in.

Psychological inventories often include questions asking if the person is a fan of made up people to see if the person is lying or not bothering to read the questions.

A woman named Shellie Kepley became concerned because she could not reach her father, Paul Gruber, despite the fact that he continued to send her greeting cards for various holidays and events. However, she had noticed that his signature was different. The next time she called him and left a message, she reminded him of her son's upcoming birthday, as well as the money he had promised. Sure enough, she promptly received a card with a check for $25. However, this only confirmed her suspicions that something was wrong, as it was NOT her son's birthday, nor had she asked him for any money, both of which her father would have known. Police later found that a local man, Darryl Kuehl, had murdered Gruber and was keeping up the illusion of him being alive by continuing to pay his bills and send letters and cards to his family.

Subversions

Anime & Manga

Death Note: L does this to Light quite a bit to see if he slips up by saying something only Kira would know. For example, showing him three suicide notes Light had some criminals write and seeing if he can find the secret message Kira inserted into them to taunt L, who has intentionally given Light the notes in the wrong order. However, Light is also a supergenius, and quickly figures out what L is up to, and hence doesn't expose himself (by putting the notes into the right order or being surprised when L introduces a fake note to the mix). Partially subverted anyway. It takes a bit for Light to realize that the fake note makes sense, and L ends up being slightly more suspicious of Light than he was before the test.

In YuYu Hakusho the heroes are told that one of them was replaced by an impostor who knows everything about the replaced person making this trope unusable. Though Yusuke still tries asking Botan her three sizes. Because, of course, she'd never told him.

In Cat-Eyed Boy, the title character shapeshifts himself into the form of a young boy to tease him. When the mother discovers this, she demands to see a birthmark she claims the boy has, and Cat-Eyed Boy assumes it's an example of this... so is the one of the pair not to have the very real identifying birthmark. Oops.

Bakugan: Gundalian Invaders. Suspicious of Jake's sudden escape from Kazarina, Shun tests him by mentioning the operation Jake participated in an earlier episode. He correctly replies that he didn't take the major role (Dan and Shun did). However, Jake was in fact brainwashed by Kazarina; she kept his memory intact.

Film

Knight Rider: In the 2008 movie, Sarah Graiman is accosted by a security guard during her escape from a pursuer. KITT warns her that the guard may in fact be a fake, and Sarah tells the guard about where she was going — except all of the locations she lists don't exist. The guard — who is a fake — catches on, however.

Ocean's Eleven: Terry Benedict, the owner of the casino the gang are trying to rob, tries this on Linus, who's disguised as a member of the Nevada Gaming Commission. It doesn't work, since Linus also has a Voice with an Internet Connection feeding him info.

Benedict: You new at the commission? Linus: Been there about two years. Benedict: I know Hal Lindley over there; you work with him at all? Linus:(beat) Not since he died last year.

In Catch Me If You Can, Frank (posing as a lawyer) claims to have been taught by a professor who also taught his girlfriend's father, and her father asks what the dog's name was. Frank, smelling a trap, replies simply that the dog had since died. The father remains suspicious.

In Kingdom of Heaven, when Balian meets his father's knights, one of them tries to discern if he really is his son. After mentioning the height, the knight goes on about the eye color of his liege, which is promptly corrected by Balian, thereby proving that he did the research, at least.

In Die Hard, John encounters Hans alone on one of the upper floors. Hans quickly pretends to be an escaped hostage, speaking in a convincing American accent instead of his usual British (well, German-ish). John introduces himself, glances at a nearby office directory and asks Hans for his name. In this case, Crazy-Prepared Hans gave a name from the directory, Bill Clay. John still somehow sees through it — a deleted scene shows he recognized the watch Hans was wearing, because it matched some of the other terrorists.

A variation in My Cousin Vinny. During the climax, Vinny puts his girlfriend Mona on the stand as an expert witness. The prosecutor demands to test her claim as an automotive expert. He asks her a question about a very specific model of car, she protests that it's a "bullshit" question. He assumes it means she's faking her expertise and tries to call her out on it. She responds that the model of car he was asking about didn't exist, corrects the question, and then answers it correctly.

Interesting Times: Rincewind, trying to hide his foreign origins on the highly-xenophobic Counterweight Continent, is asked by a suspicious restaurateur about a specific man on a specific road. He quickly declares he's never heard of the man or the road... only to find out the man is a high-ranking government official that everyone would need to deal with and the road is the main street through the capital. It works out, however, as the restaurateur is the local equivalent to CMOT Dibbler and is quite pleased to meet a foreigner.

In Night Watch, Vimes has to impersonate his (now dead) mentor John Keel in the past. His knowledge of Keel, combined with his knowledge of the events at the time and some information from the Monks of History, lets him answer the interrogating officer's questions better than the officer himself could. The interrogator assumed that the impostor is a criminal, so he starts off with questions meant to trip up a civilian and not someone who actually served as a policeman during that time. Before he can try more personal questions Vimes has him so browbeat that he does not realize that Vimes says the wrong amount when speaking of his promised wages. Vimes uses this to get more pay and a higher rank.

In Jean M Auel's Earth's Children books, Ayla is asked about the leader of the Mamutoi tribe which she tells them she has been adopted into, but she knows the fake name (Lutie) for what it is and gives the correct information ("Tulie").

In The Long Goodbye, when a woman is giving a confession that Marlowe doubts, she talks of dumping a man's body in a reservoir and Marlowe asks her how she got it over the fence. She blusters about adrenaline and then Marlowe reveals that there is no fence. After she breaks down he admits that he's never been there and really doesn't know about fence or no fence. He just thought she was lying.

In Stephen Fry's Making History, the agents try to crack Michael's story by asking him if the man he claimed to see on a train had a white or gray beard. He says that the man was clean-shaven, which turns out to be the correct answer.

In Isaac Asimov's The Union Club Mysteries, the protagonist subtly interrogates a possible spy by playing a word-match game. After several iterations, the protagonist uses a phrase from the third verse of "The Star-Spangled Banner"; the spy promptly gives the phrase that immediately follows it. The protagonist concludes that, since real Americans only know the first verse (except himself, because he knows everything), the other man is actually a spy who was trained a little too well. (Asimov was a huge proponent of knowing the entire National Anthem.)

In Trainspotting, at a job interview Renton claims to have gone to a posh secondary school, which the interviewer also went to. The interviewer then asks him if a particular teacher is still teaching there. Renton, sensing a trap, simply laughs and says "God, you're taking me back now!"

Live-Action TV

In an early episode of Burn Notice, Michael Westen gets close to a Con Man named Quention by claiming they had a mutual former cellmate, Paco, in prison. When Quentin tests Michael's cover ID, he asks about Paco's prison wine, Michael replies that "Paco doesn't drink. What are you trying to pull on me?" He and Sam lampshade this and how Michael had a Gut Feeling that Quentin was testing him and just took a shot in the dark.

When Tom Servo's evil pod clone shows up, Crow tries to discern which Servo is the real one by asking about the type of condiment Crow poured into his shoes — despite Servo having no feet — the previous week. The real Servo forgot, and the fake one correctly guesses "Was it... Ketchup?"

Servo: Damn, you are me!

Mike pulls it off by asking about Servo's collection of boxer shorts. Pod!Servo thinks this is another trick, until Servo rattles off his entire inventory in enough detail to drive the clone away in fear and "self"-loathing.

Crow: Frankly, I don't see why we need any Servo at all.

In Prison Break, Charles' first conversation with Michael is along these lines when Michael claims to have known his wife, but fails to trip him up.

There was a scene, possibly from the short-lived '90s TV series Probe, in which the hero is trying to figure out which of two men is a Soviet spy, by quizzing them about obscure sports trivia. He unmasks the spy because the guy had prepped too thoroughly for his mission and was too knowledgeable.

In Medium, when Ariel's body is possessed by the spirit of a murdered woman, Joe tries to pull this trope by suggesting an idea for her birthday party, and deliberately giving the wrong month. However, the woman in Ariel's body is prepared by now (not in the least because in a fit of desperation, Allison suggested, in front of "Ariel", that Joe ask her something only the real Ariel would know) and knows when Ariel's real birthday is (presumably from looking at her student ID). She calls him on his error, and he covers up by claiming that it's hard to keep track of everyone's birthday when you have three kids.

Leverage: Sophie is nearly outed when the mark asks her if she's familiar with a certain person. Nate smiles and tells her (on her earpiece) to reply that the man is dead, which satisfies the mark. This is a bluff on Nate's part, though, as Hardison only confirmed the information several seconds later, which would've been too late for Sophie.

For her part, Sophie tries to be as vague about it as possible invoking Never Say "Die":

Sophie: I'm so sorry. It was a beautiful ceremony.

Blackadder Goes Forth: Blackadder does this when hunting a German spy in WWI. He unmasks the spy by asking the suspect if her boyfriend had been to one of the great universities: Oxford, Cambridge, or Hull. Any real Briton would have known that only two of those are great Universities — as General Melchett remarks, "That's right! Oxford's a complete dump!" Anyway, it goes fine until it's revealed that the suspect wasn't the spy after all.

Again in Blackadder's Christmas Carol, when Pigmot asks the future Blackadder if he vanquished the Nibble-Pibblies, and the General replies "No, because you just made them up."

An episode of Fringe has Peter and Olivia infiltrating a black market biological weapons deal with an NSA agent who's been working the case feeding Olivia information through an ear bud to get around testing questions about people they should know if they are who they say they are. But Peter — who doesn't have an ear bud — is eventually asked where he met a particular individual. Olivia, with the agent's help, chimes in that they would have met at Oxford but when asked exactly where the two met neither Olivia nor the agent can help. At which point Peter, being well-traveled and brilliant, completelyimprovises a description of the scenario using his knowledge of restaurants in the area.

"The Mind of Stefan Miklos" episode of Mission: Impossible had foreign spy Simpson try to determine if the man he was talking to was really Stefan Miklos. Rollin, impersonating Miklos, not only corrected Simpson's false statements but then feigned irritation that Simpson, who was being investigated, had the gall to test Miklos.

In the Angel episode "The Shroud Of Rahmon," Angel acts like a Fan Boy to an incoming vampire and asks, "What's the password?" When the other guy says, "Password? There is no password." Angel stakes him, muttering, "Good, just checking," and goes on to impersonate him.

In the DS9 episode Whispers, Bashir is performing a medical exam on Replicant O'Brien, who's quite irritated at the length of the exam. Bashir wraps up by asking if his parents are in good health. Bashir knows that the real man's mother died two years ago and is hoping to goad the imposter into a wrong answer. But the replicant, having all of O'Brien's memories, snaps that Bashir knows full well that his mother is dead.

In House, Taub pretends to have started playing racketball regularly with Wilson, but House is almost certain he's lying and quizzes him on the sport. It's almost a double subversion in that House knows that Taub knows House is applying the trope (see the example below), but since Taub's answer was correct, he hasn't really caught him out.

Gregory House: Is a Z shot an offensive or defensive shot?

Chris Taub: Both.

Gregory House: You suspected that was a trick question.

Chris Taub: But I could have said neither.

There's a double subversion in another episode when House suspects Cuddy is feigning interest in an artist.

Gregory House: Do you prefer the pop stuff or the Venezuelan stuff?

Lisa Cuddy: That's a trick question.

Gregory House: Yes, but you don't know how it's a trick question.

In Arrow, during a flashback to his time on the island Oliver, impersonating one of Fyers' soldiers, is subjected to this with Fyers asking what boat he came in on, knowing that every soldier who comes to the island does so by airplane. Subverted in that Oliver manages to beat the bluff, but Fyers is actually already aware of who he is anyway.

Radio

In Paul Temple and the Gilbert Case, Temple and his wife agree on a question/answer which only they will know, and which she can use to challenge any telephone caller claiming to be him. In a later series - "The Spencer Affair" - they decide to use it again, but unfortunately, the bad guys have bugged their conversation. When 'Temple' next telephones, 'he' even goes so far as to remind her to use the secret question, which is then answered correctly.

Video Games

In Baldur's Gate, there is a quest that involves the player character doing investigations for Aldeth Sashenstar in his offices under the pretense of being his childhood friend. One of his business partners whose behaviour you are there to investigate (and who is himself in fact a doppleganger impostor) asks you whether, if you were Aldeth's childhood friend, you were friends with Dabron as well. Since Dabron is in truth Aldeth's real brother, it's showing ignorance that will give you away at this point, not that it makes a difference for the plot. It's not clear whether this is intended as a subversion, since the doppleganger could simply be straightforwardly trying to catch you not knowing what it's talking about... but trying to be too Genre Savvy here will certainly backfire.

Western Animation

In the SpongeBob SquarePants episode "Imitation Krabs", SpongeBob quizzes Mr. Krabs and an obvious robot impostor on things "only the really real Mr. Krabs would know". The impostor (who is obsessed with Mr. Krabs, never mind that the questions are things like "How much does a Krabby Patty cost?") jumps in with the right answer on the first two questions, while Mr. Krabs fails on the third. Doesn't help that the last question is completely bizarre and nearly impossible to follow. Of course, it is SpongeBob.

The third question is actually a trick question if you stop to think about it. Earlier in the episode, Mr. Krabs said to "never discuss the formuler". SpongeBob's question was about discussing the formula under certain circumstances, "outing" him as the impostor.

Made even better/worse in that the imposter Krabs is quite obviously a robot (complete with smoke-spewing exhaust pipes and clanking gears). It's only after Spongebob accidentally activates the self-destruct feature on the robot that he realizes that it's a fake.

Impostor: Actually, we're from the Eastern fleet. We have orders to deliver some cargo. Commander: Ah, Eastern fleet. (sarcastically) Well, nice of Admiral Chan to let us know he was sending one of his ships our way. Impostor: I'm sure Admiral Chan meant no disrespect, sir. (the commander accepts this; but later...)Commander's aide: Sir, Admiral Chan has been on leave for two months at Ember Island. Commander: What?! Why doesn't anyone ever tell me anything?

In the Transformers Prime episode Con Job, the Decepticons employ a superlative shapeshifter Transformer called Makeshift to impersonate Bulkhead's Wrecker buddy Wheeljack, who then infiltrates the Autobot base. Bulkhead suspects something's wrong all through the episode, and finally forces 'Wheeljack' to tell the story of a famous battle. Makeshift talks about a fight alongside Bulkhead and the other Wreckers, and at first it looks like he gets it right, but...

Bulkhead: Yeah, that's exactly how it happened, except for one little thing: I wasn't there.

Briefly subverted in The Transformers episode Masquerade, where five Autobots disguise themselves to resemble the Decepticon car-based team, the Stunticons, and thwart Megatron's plan. The real Stunticons escape and confront their duplicates, but Megatron is smart enough to call for the Stunticons to combine into Menasor, figuring that the Autobot fakes won't be able to do the same. The real Stunticons immediately comply, while the Autobots...merge to form their own Menasor, much to everyone's confusion. The writers were being clever here, as the team of Autobots disguised as the Stunticons includes Mirage, an expert with holograms, and Windcharger, whose special power is his ability to control magnetism. Windcharger therefore 'links' the Autobots together in the rough shape of Menasor, at which point Mirage disguises them as a copy of the real thing. It works, up until Soundwave reminds Megatron that the real Menasor will be able to access the Stunticon's own special powers and weapons.

In G.I. Joe: Renegades, Zartan impersonates Duke shortly after gaining his trademark ability. Roadblock, recalling a long story he told in the beginning, asks them for a detail about it. Unfortunately, Roadblock's story was so mind-numbingly boring that no one was paying attention, and both Dukes look at him and say they have no idea what the answer is, at the same time. Shortly thereafter, Snake Eyes, who can tell the difference because Duke and Zartan have different heartbeats, appears from nowhere and kicks the impostor in the face.

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